Mask and method of manufacturing liquid crystal display device using the same

ABSTRACT

A method for fabricating a device is disclosed. The method includes providing a substrate; forming a thin film on the substrate; forming a photoresistable layer on the thin film; irradiating light onto the photoresistable layer through a photo mask having a transmissive region, a semi-transmissive region, a diffractive region and an interceptive region, and developing the photoresistable layer to form a photoresist pattern having at least three different thicknesses. With the above-described process, a liquid crystal display device (LCD), for example, can be manufactured using three photo masks.

This application claims the benefit of Korean Patent Application No.2003-99378, filed on Dec. 29, 2003, which is hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device (LCD),and more particularly, to a mask including an optical absorption layerand a diffraction pattern and a method of manufacturing an LCD using thesame that simplifies the manufacturing process thereof.

2. Discussion of the Related Art

Liquid crystal display devices (LCD) that are a type of transmissiveflat panel display devices (FPD) are mainly applied to portableelectronic apparatuses such as notebook computers, personal digitalassistants (PDA) and mobile telephones, and are diffusively applied tohigh definition televisions (HDTV), digital televisions and thinwall-mounted televisions. In general, various kinds of FPDs such asplasma display panels (PDP), vacuum fluorescent displays (VFD) and fieldemission displays (FED), together with the above-described LCDs, areactively under study. However, due to such advantages as productivity,driving facility and high picture quality, the LCDs are mainly used.

The LCD is a device that displays information on a screen usingrefractive index anisotropy of liquid crystal. In general, liquidcrystal is provided between a lower substrate on which a driving deviceis formed and an upper substrate on which a color filter is formed toform a liquid crystal layer. The molecules of the liquid crystal layerare driven by the driving device to control the amount of light thattransmits the liquid crystal layer, thereby displaying information onthe screen. Among various kinds of LCDs, a thin film transistor (TFT)LCD in which TFTs are used as the driving device is mainly used.

The TFT is formed in each of the pixels of an LCD to independentlycontrol the pixels. Such an LCD is manufactured by complicated processesincluding a photolithography process which requires a photo mask.Therefore, simplification of the manufacturing process is a main concernin reducing the manufacturing cost and improving the yield. As a result,significant efforts have been made in order to simplify themanufacturing process. At the beginning, eight masks had been used tomanufacture a TFT-LCD. However, a seven or six mask process wasintroduced to simplify the manufacturing process, and, recently, a fivemask process has been mainly employed to manufacture a TFT-LCD.

FIGS. 1A to 1E illustrate a five mask process to manufacture an LCDaccording to a related art. A method of manufacturing an LCD will bedescribed in detail with reference to FIGS. 1A to 1E.

First, as illustrated in FIG. 1A, a gate electrode 11 made of metal isformed on a transparent first substrate 10 such as glass. Morespecifically, after forming a metal layer on the entire substrate 10,the metal layer is coated with photoresist. Then, the photoresist isdeveloped using a first mask, and an etching process is performed toform the gate electrode 11. A gate insulating film 16 is, then, formedon the first substrate 10 on which the gate electrode 11 is formed.

Next, as illustrated in FIG. 1B, a semiconductor material such asamorphous silicon (a-Si) is formed on the gate insulating layer 16 andis etched using a second mask to form a semiconductor layer 13.

Next, as illustrated in FIG. 1C, source/drain electrodes 15 are formedon the semiconductor layer 13. More specifically, after forming a metallayer on the entire semiconductor layer 13 and gate insulating layer 16,the metal layer is coated with photoresist. Then, the photoresist isdeveloped using a third mask, and an etching process is performed toform the source/drain electrodes 15. Although not shown in the drawing,an ohmic contact layer that is an impurity layer is formed between thesemiconductor layer 13 and the source/drain electrodes 15.

Next, as illustrated in FIG. 1D, after forming a passivation layer 17 onthe entire first substrate 10, a contact hole 18 is formed in thepassivation layer 17 using a fourth mask.

Then, as illustrated in FIG. 1E, a transparent electrode such as indiumtin oxide (ITO) is formed on the passivation layer 17 and is etchedusing a fifth mask such that a pixel electrode 19 is formed on thepassivation layer 17. At this time, the pixel electrode 19 is connectedto the drain electrode 15 through the contact hole 18 formed in thepassivation layer 17.

On the other hand, a black matrix 22 and a color filter layer 24 areformed on a second substrate 20, the first substrate 10 and the secondsubstrate 20 are attached to each other, and a liquid crystal layer 30is provided between the first substrate 10 and the second substrate 20to complete an LCD.

As described above, the related art method requires five masks formanufacturing an LCD: a mask for the gate electrode, a mask for thesemiconductor layer, a mask for the source/drain electrodes, a mask forthe contact hole and a mask for the pixel electrode.

Referring to FIG. 2, the above-described five-mask LCD manufacturingprocess generally uses a mask 40 having a transmissive region and aninterceptive region. The interceptive region that blocks light includesmetal patterns 42 formed on a substrate 41. The metal patterns aregenerally formed of metal such as Cr, and quartz is generally used forthe substrate 41 for high transmittance. By irradiating light onto aphotoresist layer through such a mask and then developing the phtoresistlayer, a desired pattern is formed.

Although not shown in the drawings, a photolithography process using amask is so complicated that the manufacturing cost of an LCD increasesand the yield decreases. Therefore, active efforts in reducing thenumber of a photolithography process have been made.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method formanufacturing a liquid crystal display (LCD) device that substantiallyobviates one or more of the problems due to limitations anddisadvantages of the related art.

An advantage of the present invention is to provide a mask having atransmissive region, a semi-transmissive region, a diffractive regionand an interceptive region so that three patterns are formed by oneprocess.

Another advantage of the present invention to provide a method formanufacturing a liquid crystal display (LCD) device using the mask thatsimplifies the manufacturing process thereof.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a maskincludes a transparent substrate; an optical absorption layer on thesubstrate; and a metal pattern on the substrate, the metal patternincluding a plurality of slits.

In another aspect of the present invention, a method of manufacturing aliquid crystal display device includes forming a gate electrode in apixel unit and a pad in a pad unit on a first substrate; depositing agate insulating layer, a semiconductor layer, a metal layer, and apassivation layer over the first substrate; depositing a photoresistlayer over the passivation layer; irradiating light onto the firstsubstrate through a mask having a transmissive region, ahalf-transmissive region, a diffractive region and an interceptiveregion and developing the photoresist layer to form a photoresistpattern having at least three different thicknesses; first etching thegate insulating layer, the semiconductor layer, the metal layer, and thepassivation layer over the pad to open the pad; first ashing thephotoresist pattern and second etching the passivation layer and metallayer in the pad and pixel units; second ashing the photoresist patternand third etching the passivation layer over the gate electrode; fourthetching the metal layer and a part of the semiconductor layer over thegate electrode to form source and drain electrodes; and forming a pixelelectrode.

In yet another aspect of the present invention, a mask includes atransmissive region for transmitting light, a semi-transmissive regionfor partially transmitting light, an interceptive region for blockinglight, and a diffractive region for diffracting light.

In still another aspect of the present invention, a method forfabricating a device includes providing a substrate; forming a thin filmon the substrate; forming a photoresistable layer on the thin film;irradiating light onto the photoresistable layer through a photo maskhaving a transmissive region, a semi-transmissive region, a diffractiveregion and an interceptive region, and developing the photoresistablelayer to form a photoresist pattern having at least three differentthicknesses.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIGS. 1A to 1E illustrate a five mask process to manufacture a liquidcrystal display according to a related art;

FIG. 2 illustrates the structure of a mask used for manufacturing theLCD in FIGS. 1A to 1E according to a related art;

FIG. 3 illustrates the structure of a mask according to the presentinvention; and

FIGS. 4A to 4H illustrate a method for manufacturing an LCD deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an embodiment of the presentinvention, example of which is illustrated in the accompanying drawings.

The present invention discloses a method for manufacturing a liquidcrystal display device (LCD) that simplifies the manufacturing processthereof. In particular, according to the present invention, an LCD canbe manufactured with three mask processes by employing a mask having atransmissive region, a semi-transmissive region, a diffractive regionand an interceptive region. In other words, the five mask process of therelated art can be replaced by a manufacturing method of the presentinvention, which has three mask processes or steps.

FIG. 3 illustrates a mask 140 according to the present invention. Asillustrated in FIG. 3, the mask 140 includes a transparent substrate 141such as quartz, an optical absorption layer 146 formed at apredetermined region of the substrate 141, and a metal pattern 142formed at a predetermined region of the optical absorption layer 146.The optical absorption layer 146 is made of a material that absorbslight such as MoSi. The metal pattern 142 is made of metal such as Crthat has an excellent light intercepting characteristic. As illustratedin FIG. 3, a plurality of slits 145 are also formed in the metal pattern142 to diffract incident light.

The mask 140 having the above-described structure may be divided into aplurality of regions in accordance with light transmission degrees. Forexample, the mask 140 includes a transmissive region in which the metalpattern 142 and the optical absorption layer 146 are not formed (thatis, the region in which only the substrate exists), a semi-transmissiveregion in which only the optical absorption layer 146 is formed, aninterceptive region in which the metal pattern 142 is formed, and adiffractive region in which the metal pattern 142 and the slits 145 areformed. The transmissive region transmits all incident light, and thesemi-transmissive region transmits only part of incident light (forexample, 35 to 55% of incident light). Also, the interceptive regionblocks incident light because of the metal pattern 142, and thediffractive region diffracts incident light.

When a photoresist is exposed to light through the mask 140 and isdeveloped, the photoresist pattern has three different thicknesses,because of the different regions in the mask 140. With this photoresistpattern having three different thicknesses, an LCD device can bemanufactured using three mask processes or steps. Although the presentinvention is explained with an example of a manufacturing process for anLCD device, it should be appreciated that the principles of the presentinvention can be applicable to a manufacturing process for other devicesthat requires a photolithography process.

Hereinafter, a method for manufacturing an LCD device using theabove-described mask will be described in detail with reference toattached drawings.

FIGS. 4A to 4H illustrate a method of manufacturing an LCD deviceaccording to the present invention. In the drawings, a pixel unit isseparated from a pad unit for convenience sake.

First, as illustrated in FIG. 4A, after depositing metal such as Al, anAl alloy, and Cu on a transparent first substrate 110 such as glass byan evaporation method, a sputtering method, or the like, the metal layeris etched using a first mask to form a gate electrode 111 in the pixelunit and a pad 151 in the pad unit. Then, a gate insulating layer 116, asemiconductor layer 113 a, a metal layer 115 a, and a passivation layer117 are continuously formed on the entire first substrate 110.

The gate insulating layer 116 is formed of an insulating material suchas SiNx and SiOx. The semiconductor layer 113 a further includes aundoped silicon layer formed of, for example, amorphous silicon (a-Si)or crystalline silicon and an impurity layer doped with impurity ions.Also, the metal layer 115 a is formed by depositing metal such as Mo andan Mo alloy by an evaporation method, a sputtering method, or the like.The passivation layer 117 is formed of either an inorganic material suchas SiNx and SiOx or an organic material such as benzocyclobutene (BCB)and photoacryl.

Next, as illustrated in FIG. 4B, a photoresist layer 162 a is formed onthe first substrate 110 on which the gate insulating layer 116, the semiconductor layer 113 a, the metal layer 115 a, and the passivation layer117 are formed. Then, light such as ultraviolet (UV) rays is thenirradiated onto the photoresist layer 162 a through the mask 140, whichhas the transmissive region, the semi-transmissive region, thediffractive region and the interceptive region in accordance with thepresent invention. After the photoresist layer 162 a is developed usinga developer, a photoresist pattern 162 having different thicknesses isformed on the passivation layer 117. In this example, the transmissiveregion of the mask 140 is positioned over the pad 151 of the pad unit,and the diffractive region is positioned over the gate electrode 111.Also, the interceptive region is positioned at both sides of thediffractive region, and the semi-transmissive region is positioned inthe pixel unit excluding the areas of the transmissive region and theinterceptive region. During the developing process, the photoresistlayer on the pad is removed, and the photoresist pattern 162 having thethicknesses of t1, t2, and t3 (t1<t2<t3) is formed on the passivationlayer 117 of the pixel unit.

Next, when a dry-etching process is performed to remove the passivationlayer 117, the metal layer 115 a, and the gate insulating layer 116 onthe pad 151, on which the photoresist pattern 162 is not formed, acontact hole 153, which is exposed to outside, is formed on the pad 151,as illustrated in FIG. 4C.

Next, an ashing process is performed using plasma ions to remove apredetermined portion or thickness of the photoresist pattern 162. As aresult, only the photoresist pattern 162 over the gate electrode 111 andthe photoresist pattern 162 at both sides of the gate electrode 111 inthe pixel unit remains on the first substrate 110. Then, a dry-etchingprocess is performed to remove the passivation layer 117 and the metallayer 115 a of the pixel unit and the pad unit excluding the regions inwhich the photoresist pattern 162 remains on the first substrate 110.During the etching process, the metal layer 115 a formed of Mo or an Moalloy is removed, while the pad 151 formed of Al or an Al alloy, whichis also exposed to the etching condition, is not affected by the dryetching process.

Next, another ashing process is performed to remove the photoresistpattern 162 over the gate electrode 111 such that only the photoresistpattern 162 at both sides of the gate electrode 111 remains on the firstsubstrate 110, as illustrated in FIG. 4D. Then, a dry-etching process isperformed to remove the passivation layer 117 on the gate electrode 111to expose the metal layer 115 a, as illustrated in FIG. 4E, and removethe semiconductor layer 113 a of the pixel unit and the pad unitexcluding the regions blocked by the metal layer 115 a, as illustratedin FIG. 4F. Then, a dry-etching process is continuously performed toremove the metal layer 115 a and part of the semiconductor layer 113(that is, the ohmic contact layer) on the gate electrode 111, and then,the photoresist pattern 162 is removed, thereby forming source/drainelectrodes 115, as illustrated in FIG. 4G. During the etching process,the metal layer 115 a formed of Mo or an Mo alloy is removed, while thepad 151 formed of Al or an Al alloy, which is also exposed to theetching condition, is not affected by the dry etching process.

Then, as illustrated in FIG. 4H, after forming a transparent conductivelayer such as indium tin oxide (ITO) or indium zinc oxide (IZO) on theentire first substrate 110, a photolithography process is performedusing a third mask to a pixel electrode 119 in the pixel region and anoxidation preventing layer 153 on the pad 151 in the pad region. Becausethe source/drain electrodes 115 are formed of Mo or an Mo alloy, thesource/drain electrodes 115 have an excellent side contactcharacteristic. Therefore, as illustrated in the drawing, the pixelelectrode 119 can be connected to the side of the drain electrode 115.

On the other hand, Cr/CrOx or black resin is formed on the secondsubstrate 120 to form a black matrix 122 for preventing light leakage,and a color filter layer 124 having red (R), green (G), and blue (B)layers is formed on the second substrate 120 for color implementation.Then, after the first substrate 110 and the second substrate 120 areattached to each other using sealant, a liquid crystal layer 130 isprovided between the first substrate 110 and the second substrate 120 tocomplete a liquid crystal display.

As described above, according to the present invention, it is possibleto manufacture an LCD device with three masks: a mask for the gateelectrode, a mask for the semiconductor layer and the source/drainelectrodes, and a mask for the pixel electrode. The second mask used forpatterning the semiconductor layer and the source/drain electrodes has atransmissive region, a semi-transmissive region, a diffractive regionand the interceptive region to differentiate the amount of light thatpasses through the second mask. Due to the different regions of thesecond mask, a photoresist pattern has various thicknesses. As a result,an LCD device can be manufactured by a three-mask process.

A photo mask according to the present invention is not only applicableto a manufacturing method for a TN-LCD device (typical LCD device), butis also applicable to other LCD devices, such as an in plane switching(IPS) mode LCD and a vertical alignment (VA) mode LCD. Further, theprinciples of the present invention can be applicable to a manufacturingprocess for other devices that requires a photolithography process.

As described above, according to the present invention, because an LCDdevice is manufactured with a photo mask having a transmissive region, asemi-transmissive region, a diffractive region and an interceptiveregion, it is possible to reduce the number masks and simplify themanufacturing process.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of manufacturing a liquid crystal display device,comprising: forming a gate electrode in a pixel unit and a pad in a padunit on a first substrate; depositing a gate insulating layer, asemiconductor layer, a metal layer, and a passivation layer over thefirst substrate; depositing a photoresist layer over the passivationlayer; irradiating light onto the first substrate through a mask havinga transmissive region, a half-transmissive region, a diffractive regionand an interceptive region and developing the photoresist layer to forma photoresist pattern having at least three different thicknesses; firstetching the gate insulating layer, the semiconductor layer, the metallayer, and the passivation layer over the pad to open the pad; firstashing the photoresist pattern and second etching the passivation layerand metal layer in the pad and pixel units; second ashing thephotoresist pattern and third etching the passivation layer over thegate electrode; fourth etching the metal layer and a part of thesemiconductor layer over the gate electrode to form source and drainelectrodes; and forming a pixel electrode.
 2. The method according toclaim 1, wherein the metal layer is formed of Mo or an Mo alloy.
 3. Themethod according to claim 2, wherein the metal layer is etched by a dryetching.
 4. The method according to claim 2, wherein the pixel electrodeis connected to a side portion of the drain electrode.
 5. The methodaccording to claim 1, wherein the method of manufacturing a liquidcrystal display device uses three photo masks.